The present invention relates to a method for producing diallyl ester of an aromatic dicarboxylic acid having an excellent transmissivity by ester-exchange reaction between dialkyl ester of the aromatic dicarboxylic acid and allyl alcohol, particularly a novel method for obtaining diallyl esters of a symmetrical aromatic dicarboxylic acid at a high yield.
Polymerization product of diallyl ester of a symmetrical aromatic dicarboxylic acid, for instance, that of diallyl terephthalic acid, is excellent in electric properties, dimensional stability, heat resistance, weather-proofness, resistance to chemicals and mechanical properties as compared to the polymerization product of diallyl ester of non-symmetrical aromatic dicarboxylic acid and accordingly, the former has been broadly utilized as electrical material, mechanical material and construction material. Further, recently, it has been found that the above-mentioned polymer is also excellent in optical properties such as transparency, refractive index and surface hardness, and the polymer is expected as optical material.
As the conventional method for producing diallyl ester of aromatic dicarboxylic acid, the following methods have been known:
(1) a method of directly esterifying aromatic dicarboxylic acid with allyl alcohol, PA1 (2) a method of condensing metal salt of aromatic dicarboxylic acid with allyl halide in the presence of tertiary amine as a catalyst in an aqueous medium or in an anhydrous reaction system, and PA1 (3) a method of ester-exchange reaction between ester of aromatic dicarboxylic acid and allyl alcohol.
However, the method of direct esterification (1) proceeds slowly and so it is necessary to carry out the reaction at a high temperature for a long time period accompanied by unfavorable phenomena such as polymerization of allyl alcohol and colouring of the reaction product. Moreover, the reactivity of symmetrical aromatic dicarboxylic acid and allyl alcohol in the direct reaction is unfavorably poor.
The method for producing diallyl ester of aromatic dicarboxylic acid according to (2), that is, by condensation of them, has been and is now most generally adopted, however, the method has its demerits as follows: in the case where the reaction is to be carried out in an anhydrous system, its necessitates troublesome processes such as condensing and drying the metal salt of aromatic dicarboxylic acid prepared in an aqueous solution. In addition, in the case where the reaction is carried out in an aqueous medium, by-products derived from hydrolysis of allyl halide are apt to be formed, and accordingly, there are problems of separation of by-products and purification of the main product. Moreover, the metal salt of symmetrical aromatic dicarboxylic acid which is used as a starting material for producting allyl ester of the symmetrical aromatic dicarboxylic acid is hard to be synthesized and accordingly, the method has not yet been adopted on industrial base.
On the other hand, the method (3), that is, by ester-exchange, has attracted the attention of those skilled in the art as a method for which the starting materials are easily available and which can be carried out under mild reaction conditions. However, the use of a catalyst in the above-mentioned ester-exchange reaction is indispensable, and it is no exaggeration to say that the industrial values such as the productivity, cost, etc. are mainly determined by the result of selection of the catalyst. Hitherto, as a catalyst for use in the above-mentioned reaction, sodium methoxide, metallic magnesium, tetrabutyl titanate, organic tin compounds, etc. have been known. According to the results of tracing experiment on the above-mentioned method by the inventor of the present invention, the above-enumerated catalysts have demerits in the ester-exchange reaction (with ester of symmetrical aromatic dicarboxylic acid and allyl alcohol) such as their lower catalystic activity not to give a high yield and the tendencies of formation of by-products, polymers and colouration. So, it is an important problem to develop a catalyst for use in producing diallyl ester of aromatic dicarboxylic acid, particularly of symmetrical aromatic dicarboxylic acid, of high in activity and effective in suppressing the side-reactions such as polymerization.
The inventor of the present invention, after having studied the above-mentioned problem, has found that a specific catalyst specifically accelerates the reaction of ester-exchange between ester of aromatic dicarboxylic acid and allyl alcohol while suppressing the side-reactions such as polymerization and addition, thus giving the intended product at a high yield, and has attained the present invention.
It is an object of the present invention to provide a method for producing a diallyl ester of an aromatic dicaboxylic acid, comprising heating an ester of an aromatic dicarboxylic acid and allyl alcohol at a temperature of 100.degree. to 200.degree. C. in the presence of a mixture consisting essentially of one part by mole of catalyst(A) and 0.01 to 5 parts by mole of catalyst(B), the catalyst(A) being at least one organic tin compound of the formula (I): ##STR2## where R.sup.1 and R.sup.2 respectively represent an alkyl group of 1 to 8 carbon atoms or a phenyl group, and X represents two halogen atoms or an oxygen atom and the amount of the organic tin compound being 0.3 to 5 mole % of the ester of the aromatic dicarboxylic acid, the catalyst(B) being at least a simple substance of or a compound of a metallic element selected from the group consisting of magnesium, zinc, tin, lead, aluminum, nickel and zirconium.